1. Field of the Invention
The invention relates to an improved FED driving method, which uses a voltage control different from the prior FED, to turn an electron beam on/off, increase the resolution and lighting efficiency.
2. Description of Related Art
FIG. 1 is a diagram of a typical FED structure formed by thin film technique. In FIG. 1, the typical FED structure is a triode structure: a gate 5, an anode 9 and a cathode 10 including microtips 2 located in respective emitter cavities 3. As shown in FIG. 1, the triode structure is a structure capable of increasing electronic energy and lighting efficiency and reducing control voltage, wherein the anode 9 is applied to about 7 kV to increase electronic energy, the microtips 2 grounded in the cathode 10 emit the electron beams 4, and the gate 5 is applied to about 200V (or less) to pull out the electron beams 4 from microtips 2 of the cathode 10. Such a structure can have higher lighting efficiency due to the high anode voltage on anode 9 (for example, about 7 kV as mentioned above). However, it also has the disadvantages of high cost and low life duration on the microtips 2 so that does not fit for a large-sized panel display manufacture.
FIG. 2 is a diagram of another typical FED structure formed by nanotechnology. In FIG. 2, the structure is the same as that of FIG. 1 except that the microtips 2 are replaced by the low work function electronic emitters 6 (i.e., the needle-like arrangement in the respective emitter cavities 3). As shown in FIG. 2, such a structure has low work function such that the electronic emission requirement from the electronic emitters 6 is about 2-3 V/um, much less than the requirement from the micrptips 2 (about 70-80 V/um) The height of the spacer 8 connected between the anode 9 and the cathode 10 influences the required anode voltage for pulling the electrons out of the electronic emitter 6. In an example of the spacer 8 with about 1 mm height, the anode 9 in FIG. 1 with the microtips needs about 70-80 thousand volts to produce the electron beam. Generally, the anode voltage is not so high, only several kilo Volts, so need the gate to pull the electrons. While the anode 9 in FIG. 2 with the low work function electronic emitters needs only about 2-3 kV to produce the electron beam from the cathode, the gate losses the electron-pulled function and cannot turn the electron beam on/off. To recover the electron beam on/off control, the anode voltage is reduced. However, this causes lower lighting efficiency. Further, if the height from the electronic emitter 6 to the anode 9 is increased, the anode voltage can increase up to the lighting efficiency as in FIG. 1 under the same driving conditions and the gate can turn the electron beam on/off at the same time. However, the increased height makes a larger scattering area due to the gate""s lateral attraction, when the electron beam hits the anode plate, so as to reduce the resolution.
A summary of adjusting a typical FED structure driving method by the factors of resolution and lighting efficiency is shown in the following relationship.
1. A method of increasing lighting efficiency is: increasing the anode voltage and the spacer height between the anode and the cathode. However, this causes the electron beam""s divergence by the gate""s lateral attraction and reduces the resolution. The spacer is higher, the resolution lower.
2. A method of increasing resolution is: fixed spacer height with an increased anode voltage to enhance the verticality of the electron beam emitted and reduce the gate voltage in order to decrease the beam""s divergence. However, this will loss the gate""s control over to the electron beam.
As cited above, the typical FED triode structure""s driving method cannot have high lighting efficiency and high resolution when using a low work function electronic emitter.
Accordingly, an object of the invention is to provide an improved FED with low work function electronic emitters driving method, which uses a voltage control different from the prior triode FED, to turn an electron beam on/off and increase the resolution.
The invention provides an improved FED driving method, which uses a voltage control method by a combination of diode driving and gate control, so as to increase resolution and maintain electron beam on/off control. The improved FED driving method is characterized in increasing a positive voltage applied to the FED""s anode, grounding the FED""s emitter and applying a negative voltage to the FED""s gate. When driving the FED, the anode can pull the electron beam out of the cathode and the applied negative voltage on the gate can turn the electron beam on/off. As such, this allows a higher resolution because the electron beam is not influenced by the gate""s lateral attraction and high lighting efficiency with high anode voltage.